Farmers Assess Impact of Recent Heat Wave

It will be weeks, if not months, before California farmers can fully assess the impacts of the late spring/early summer heat wave that affected many of the state’s agricultural regions.

Farmers of some crops expect to see an effect—though the extent won’t be certain until harvest.

“I think we’re likely to see some reduced yields, based on blossom drop or smaller fruit, and possibly sunburn,” said Bruce Rominger, a processing-tomato farmer in Winters.

Some tomatoes are only a couple of weeks from harvest, he said, while others were planted around the beginning of June and remain young. Rominger said the key is consistent irrigation.

“You can’t all of a sudden irrigate more and make up for it,” he said. “You just have to keep the same irrigations to make sure the plant has the moisture.”

Rominger said he won’t know how his tomatoes fared until they reach the processing plant.

“We have to wait until harvest,” he said. “We know there will be some effect. We don’t know the scale of it.”

The duration of the heat is the main factor in tomato damage, said Gene Miyao, a University of California Cooperative Extension farm advisor.

“It’s not just hitting a temperature spike for half an hour,” Miyao said. “That isn’t as problematic as having hours on end of these hundred-degree-plus temperatures.”

The main damage will come from plants losing flower blooms because of a lack of wind pollination, he added.

“Some of the plants could recover a bit, but if they’re in this plant-growth stage of the most abundant flowers on the vines, then recovering from that is unlikely,” Miyao said.

He credited tomato-plant breeders with developing varieties better able to withstand heat, and said the recent weather could help them refine their research.

“If there’s some good things that can come out of it, I’d say we’re going to get the potential for identifying heat-tolerant varieties, to a degree,” Miyao said.

Jim Peterson, who grows almonds, walnuts and pistachios in Colusa County, said the trees enjoy the warmth—up to a point.

“That point’s somewhere around 90 degrees,” Peterson said. “Once you get close to 100 degrees, those trees stop photosynthesizing and they start going into transpiration, where it’s just pulling water through the tree to cool itself down. Once you get to 105 degrees, then the tree starts killing itself to keep it alive”—meaning the tree will start shedding its crop as a result of the heat.

Besides running extra water, Peterson also applied a sun protection material to the trees to prevent the nuts and leaves from sunburn. The product is important but expensive, he said.

“In the next couple of weeks, we’ll start to see the effects of the heat spell,” Peterson said, adding that if the tree went into survival mode, proper nutrients aren’t reaching the nuts, which could result in lower yields and poor quality.

“You can plan for it by making sure you have plenty of water and that the trees are in good health,” he said. “If they’re in really good health, it helps mitigate it, but there isn’t a whole lot you can do when temperatures get to a certain point.”

The heat largely bypassed the coast, although farmer David Schwabauer of Moorpark was irrigating more than usual to keep his avocado groves well hydrated.

“We’ve got a nice crop on the trees, and warm weather turning into really hot weather will stress the trees, so we’ve got to be really careful and make sure we keep the irrigation water going and the trees moist, so that they don’t drop next year’s crop because of the heat,” Schwabauer said.

His 2017 avocado crop has already been picked, he said. Crews working the lemon orchards were starting their workdays as early as possible to avoid the worst heat. The only hitch is that if Ventura County’s coastal fog reaches inland and lemons are picked while they’re wet, oil vesicles on the rind will bruise and the fruit will start to rot.

“The guys may show up early, but then you have to wait until Mother Nature dries the fruit off before you can start picking,” Schwabauer said.

The 2017 heat wave evoked memories of 2006, when a hot spell nearly two weeks long killed thousands of dairy cows. Dino Giacomazzi, a Hanford dairy farmer, said he and others have been applying lessons learned from that disaster.

“We have been working very hard over the last decade to continuously improve our cow comfort operations: shade, soakers, things like that,” he said.

Cows can begin experiencing heat stress at about 80 degrees, he said, as they begin using most of their energy to cool themselves by respiration. They also stop eating, which leads to a decrease in milk production, and fertility declines, as cows aren’t as likely to get pregnant in such conditions.

Overnight temperatures need to drop into the 60s to help cows recover, and Hanford cooled into the 70s most nights last week—not ideal but nowhere close to 2006 levels, he said.

Giacomazzi said heat knowledge has progressed in the 10-plus years since the devastating losses of 2006.

“Since then, most people have updated their facilities and improved the conditions for the cows,” he said, “so hopefully we won’t have that kind of event again.”

At the National Weather Service office in Sacramento, Jim Mathews said it’s too soon to know exactly what will happen this summer—but he figures Californians haven’t seen the last of the heat. The NWS Climate Prediction Center map shows a 50 percent probability of above-average temperatures for most of California.

“It would certainly suggest, anyway, that we’re in for a couple of prolonged heat waves for the rest of the summer,” Mathews said.

Kevin Hecteman is an assistant editor of Ag Alert. He may be contacted at khecteman@cfbf.com. Permission for use is granted by the California Farm Bureau Federation when reprinting this item.